the missile system which the u.s. helped develop has been knocking rockets out of the sky. instantly, radar detects a rocket's trajectory, firing an intercepting missile. so far the system has knocked out over 300 rockets, with a stunning 90% kill rate. israel has authorized the call-up of 75,000 reserves. tanks are already massing on gaza's border. another one of the sirens is just going off. this has been happening all day here. driving around, you see people trying to take shelter under the buildings and i'm going to pull over right now, too. some of the rockets get through. this one punched through several stories of this building and into alex's apartment. he didn't notice the sirens. his dog did. barking incessantly and forcing him to leave the room, a move he says saved his life. i want you to see this hunk of shrapnel. which penetrated a safe room on the second story. now, to give you a sense of the symmetry of cost here. the rocket that this came from, likely cost about $500. now, the iron dome missile sent to intercept it, $100,000. david? >> matt gutman tonight,